1. Field of the Invention
The present invention relates to an image forming apparatus represented by a copying machine, a printer, a printing press, or the like and, more particularly, to an image forming apparatus including an endless belt-shaped transfer belt facing a plurality of image carriers.
2. Description of the Related Art
Along with an increase in speed of image forming apparatuses, dominating arrangements employ a plurality of image carriers facing an endless belt-shaped transfer belt and parallelly execute the image forming processes of the respective colors. For example, toner images of the respective colors are transferred to a transfer belt that is an endless belt in a superimposed manner, and the superimposed toner images are at once transferred to a printing material. The endless belt loops over a plurality of rollers and is driven by these rollers. The endless belt shifts in a direction perpendicular to the moving direction due to the diametral accuracy of the rollers or the alignment accuracy between the rollers.
Japanese Patent Laid-Open No. 2002-287527 discloses an arrangement for controlling the belt shift by detecting a variation in the position of a belt end face and adjusting, in proportion to the detected variation, the tilt of an adjustment roller that is one of the rollers to loop the belt.
In the arrangement described in Japanese Patent Laid-Open No. 2002-287527, however, changing the tilt of the adjustment roller causes a variation in the main scanning direction, that is, the direction perpendicular to the direction in which the belt should move. This may lead to an increase in color misalignment.